1. Field of the Invention
The present invention relates to a positive resist composition. More particularly, the present invention relates to a positive resist composition which is sensitive to ultraviolet light, far ultraviolet light (including excimer laser), electron beam, ion beam, X-ray and the like.
2. Description of the Related Art
Recently, with a rise in the integration level of integrated circuits, formation of patterns of submicron order is required, and it is desired to provide a positive resist composition which is excellent in various properties such as depth of focus, profile, developing residue (scum), heat resistance, sensitivity and resolution. In particular, for the production of 16-64 MDRAMs, it is necessary to resolve a pattern having a line width of 0.5 .mu.m or less with a good profile and a broad depth of focus.
The resolution can be improved by, for example, increasing the amount of a sensitizer. However, this method will increase the amount of scum undesirably. To improve the resolution without increasing the amount of scum, the use of a novolak resin having a specific molecular weight distribution is proposed (cf. Japanese Patent Kokai Publication No. 105243/1989 corresponding to U.S. Pat. No. 4,812,551). However, this method is insufficient in view of the depth of focus.
Hitherto, it has been very difficult to resolve patterns having line widths of 0.5 .mu.m or less with a good profile and a broad depth of focus.